Used in the development of antibody-drug conjugates (ADCs) as a cleavable linker that connects cytotoxic drugs to monoclonal antibodies. The linker system allows for controlled release of the drug inside target cells through enzymatic cleavage by cathepsin B in lysosomes. The PAB (para-aminobenzyl) spacer enables efficient drug release after cleavage, while the PNP group acts as a self-immolative unit. This design enhances the specificity and efficacy of ADCs in cancer therapy by minimizing off-target toxicity and improving plasma stability. Widely applied in oncology research and in the formulation of targeted therapeutics.